The invention relates to a stacker for mail and similar flat, flexible conveying material.
In automatic mail distribution systems, the mail is transported individually on a conveying path for the purpose of automatically reading its destination and later sorting it accordingly. The mail is assigned, by way of a compartmented path equipped with switches, to a plurality of stack compartments according to postal code regions.
In order to obtain the highest possible throughput, the mail moves on the conveyor belt at the greatest possible speed and with the smallest possible spaces between individual articles. Under these circumstances, mail that is assigned to the same stack compartment encounters the problem of congestion caused by the leading edge of the next-following article running onto the trailing edge of the preceding article.
German Offenlegungsschrift DE-OS No. 3,317,865 discloses a mail distribution system for articles of mail that are stacked upright so as to rest on their lower longitudinal edges to guide such articles, when they enter the equipment, so that their lower leading edge enters tangentially into a revolving spindle wheel. In the course of the article entering the stack compartment, the edge of the spindle wheel transports the subsequent portions of the article, particularly its trailing region, in the direction of the already stacked articles so that the next-following article will reliably enter the stack compartment next to the preceding article.
However, a spindle wheel drive for each stack compartment is very complicated and expensive, particularly for fine distribution systems having a large number of small capacity stack compartments and a low throughput.
According to German Offenlegungsschrift DE-OS No. 3,700,827, a pressure roller is provided which is disposed below the contact surface of the incoming articles and which grips the lower edge of the incoming letters with part of its upper roll circumference so as to urge them in the direction of the stack of letters.